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  • Writer's pictureGTT Commercial Tires

Tire Codes: What They Are and How To Read Them

As a trucker, you've seen the writings on the side of your tires, but they're not just manufacturing gibberish. Each tire code actually has significant meaning that every trucker should familiarize themselves with to make knowledgeable purchasing and safety decisions.



Tire Code Overview:
Tire Code Guide: How to Read Tire Codes

Tire Size Code

Tire Code for Tire Sizes: How to Read Them





1st Number = Tire Width

Represents the tire width (mm) from one shoulder to the other (the width of the tire’s road contact patch)

2nd Number = Tire Aspect Ratio

Indicates the tire’s sidewall height from the rim to the tread

3rd Number = Rim Diameter

The distance measured between the parallel bead seats of a wheel


After the second number, there can be a letter R, D, or a dash (–).

Radial (R):

Plies are placed at 90-degree angles from one to the other sidewall which optimizes the tires for everyday use, as it minimizes the possibility of heat build-up.

Diagonal (D):

Nylon cord casing layers are placed diagonally in the tread and sidewall. These typically belong to trailer tires for load bearing.

Bias-Ply (–):

Internal ply cords are diagonally placed, overlapping each other, and angled at 30-40 degrees in order to reinforce the tire’s strength.


Load Index

Load index determines how much weight one tire can handle and corresponds to the specific weight (pounds) the tire withstands while still offering secure performance.


Fundamental rule when replacing tires: Never go lower on the load index.


Speed Ratings

Located After the load index & indicates the tire’s maximum speed capability

Below is a chart depicting each speed rating, the max speed, and the vehicle type for each.

Speed Rating

Max Speed (mph)

Vehicle Type

L

75

Off-road, light truck

M

81

N/A, temporary spare

N

87

N/A, temporary spare

Q

99

Winter 4x4

R

106

Heavy-duty light truck

S

112

Family sedan, van

T

118

Family sedan, van

U

124

Sedans, coupes

H

130

Sport sedans, coupes

V

149

Sports cars

Z

149+

Sports cars

W

168

Exotic sports cars

Y

186

Exotic sports cars


Uniform Tire Quality Grading (UTQG)

Treadwear Grade

Provides a better look into the expected tread life of the specific tire model.

For example, if the treadwear grade is 280, the tire’s excepted tread life is around 28,000 miles

Traction Rating

Represents the tire’s ability to stop on wet road surfaces. The better this rating is (with AA being the best), the shorter its stopping distance will be.

Temperature Grade

Indicates the tire’s heat durability. Ranges from A-C, with “A” withstanding the highest temps.


Weather Durability

All-Season:

Tires that feature M+S on their sidewalls are all season models. This indicates their performance in mud and snow, basically rainy and snowy conditions.

Winter Tires:

Depict the 3PMS (three-peak mountain and snowflake) symbol, showcasing the tire’s secure application in freezing and icy situations.


Use this post as a guide to refer back to when buying or even inspecting your tires to ensure you have the tires you need for your specific application.

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